docs: def deprecated(message=None):
      """Decorator to mark functions as deprecated. A warning will be emitted when the function is used."""
      def deco(func):
          @functools.wraps(func)
          def wrapped(*args, **kwargs):
              warnings.warn(
                  message or 'Call to deprecated function {}'.format(func.__name__),
                  category=PubChemPyDeprecationWarning,
                  stacklevel=2
              )
              return func(*args, **kwargs)
          return wrapped
      return deco